Water reactive alloy



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United States Patent WATER REACTIVE ALLOY Otto T. Pfelferkorn, Arcadia,Calif. Application March 24, 1952, Serial No. 278,284 4 Claims. (Cl.75-134) (Granted under Title 35, U. S. Code (1952), see. 266) Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the pay ment of any royalties thereon or therefor.

This invention relates to a water reactive fuel for use in devices ofthe type wherein energy produced by the reaction between fuel and wateris utilized.

Desirable characteristics of Water reactive fuels are high heat energycontent per unit volume, low melting point, inexpensiveness, and usablereaction products. A number of water reactive fuels have been tested inthe past with varying success. An alloy containing about 25% sodium and75% potassium has long been used in experimental work. Thesodium-potassium eutectic melts at near 20 F, is relatively very cheap,and is easy to handle, but the heat of hydrolysis is only 1.25 K.cal./cc. The use of lithium has been considered in spite of its highmelting point, corrosiveness, and high cost because lithium has a heatof hydrolysis of 3.7 K. caL/cc.

It has now been discovered that a water reactive alloy containinglithium, aluminum and a small proportion of a strong alkali metal has ahigher total energy of reaction per unit volume than lithium. Theignition temperature of the fuel with water is lower than that oflithium with water, and the use of low cost aluminum brings the cost ofthe new alloy well below that of lithium. The aluminum which has a heatof hydrolysis of 9.6 K. caL/cc. serves to increase the total energycontent of the alloy, and the strong alkali metal decreases the alloymelting point, promotes smoother burning, and provides positiveignition.

An object of this invention is to provide improved fuels whereinaluminum, lithium, and a strong alkali metal are alloyed to form highenergy, low melting point, water reactive mixtures.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following description.

The single figure shows the constitution diagrams of aluminum andlithium plus a strong alkali metal such as sodium or potassium.

In the diagram, line represents lithium-aluminum alloys. The meltingpoint of pure lithium which is about 365 F. decreases slightly with theaddition of a few per cent of aluminum until a eutectic point isreached. As more aluminum is added, the melting point rises sharply.Line 12 represents the melting point of lithium plus 5% of sodium basedon total weight of alloy as increased amounts of aluminum are added. Thelithiumsodium alloy has a melting point of about 350 F. which isincreased only slightly by the addition of up to more than 20% ofaluminum by weight. To obtain the advantages of inexpensiveness and highenergy content of aluminum to the greatest extent possible without thenecessity of employing high preheat temperatures with attendantcorrosion and piping problems, a preferred composition contains 74%lithium, 5% sodium, and 21% aluminum. Line 14 represents the meltingpoint of lithium plus 5% of potassium based on total weight of alloy asincreased amounts of aluminum are added. On

timum proportions for alloys may be obtained from the constitutiondiagram. Representative data in the following table demonstrate theeffect of varying the concentration of alkali metal.

Sodium is the least expensive of the alkali metals, and it also has thegreatest energy per unit volume. The teats of hydrolysis of sodium,potassium, rubidium, and cesium are 1.84, 0.94, 0.8 and 0.68 K. cal./cc.respectively.

The alloys of the instant invention may conveniently be prepared bymelting lithium with the alkali metal under a blanket of a dry inert gassuch as helium or argon and then adding with agitation the desiredamount of aluminum which readily disperses in the very fluidlithiumalkali metal mixture. The described alloys are sufiiciently fluidto be pumped and nozzle injected at any temperature above the meltingpoint. Such fuels are commonly preheated to about 50 F. above theirmelting point before injection into the water-containing reactionchamber, at which temperature the alloys are mobile.

It will be evident that the invention is not limited to any specificproportions and that the percentage of strong alkali metal present inthe alloy may be varied.

The alloys of the instant invention are useful in the field ofhydropropulsion, in compact steam generators, and the like.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A water reactive composition consisting of lithium mixed with 1% to25% by weight of aluminum and 1% to 10% by weight of an alkali metalfrom the group consisting of sodium and potassium.

2. A composition melting below 400 F. capable of reacting with waterwhich consists of from 1% to 25% sodium, 1% to 25 aluminum, and 65% tolithium.

3. A water reactive composition consisting of lithium as the majorcomponent, from 1% to 23% of aluminum, and a proportion of an alkalimetal from the group con sisting of sodium and potassium effective tolower the melting point of said composition below 400 F.

4. A composition containing 74% lithium, 21% aluminum, and 5% sodium.

References Cited in the file of this patent UNITED STATES PATENTS909,536 Brindley Jan. 12, 1909 1,532,930 ONeill Apr. 7, 1925 1,620,081Czochralski Mar. 8, 1927 2,573,471 Malina et al. Oct. 30, 1951 OTHERREFERENCES Leonard: Some Possibilities For Rocket: Propellants,published in Journal of the American Rocket Society, December 1947,pages 10-23.

1. A WATER REACTIVE COMPOSITION CONSISTING OF LITHIUM MIXED WITH 1% TO25% BY WEIGHT OF ALUMINUM AND 1% TO 10 % BY WEIGHT OF AN ALKALI METALFROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM.